Major uses of mono-alkylphosphines include uses as chemical intermediates and in semiconductor fabrication. For production of mono-alkylphosphines to be used as chemical intermediates, it is desirable to have a process to make the mono-alkylphosphines in high chemical yield and specificity of mono-alkylated over di-alkylated or tri-alkylated phosphines or other products.
Mono-alkylphosphines, especially mono-tertiary-butylphosphine, are also useful in the manufacture of semiconductor devices such as solar cells and computer chips produced through processes such as metalorganic chemical vapor deposition (MOCVD) and other processes and which require volatile sources of phosphorus as reactants therein. Mono-alkylphosphines for use in semiconductor applications must be of high chemical purity, containing minimum amounts of stereoisomers or other chemical compounds and, especially, substantially no metallic or oxygenating impurities. Use of such very high purity monoalkylphosphines makes possible the fabrication of high quality semiconductor materials without the toxicity and environmental hazards associated with the use of phosphine gas, which has been the typical volatile source of phosphorus used in semiconductor fabrication. Therefore, a process is needed to make very high purity mono-alkylphosphines, containing substantially no metallic or oxygenating impurities.
The production of alkylphosphines typically involves reaction of a Grignard reagent or other organometallic reagent with phosphorus trichloride to produce an alkylated phosphorus halide derivative, which is then converted to the alkylated phosphorus hydride (alkylphosphine) by reaction with such substances as NaBH.sub.4,LiAlH.sub.4, or Zn/HCl.
Alternatively, the appropriate olefin typically has been reacted with phosphine in the liquid phase using either acid or free radical catalysts.
For example, U.S. Pat. No. 2,584,112 discloses a process for the preparation of mono-alkylphosphine by condensing phosphine with an olefin in the presence of a strong non-oxidizing acid catalyst. Noted catalysts include alkyl- and aromatic-sulfonic acids, liquid HF, F.sub.3 CCOOH, BF.sub.3 and H.sub.3 PO.sub.4 --P2O.sub.5.
Hoff, M.C. and Hill, P.(JACS 24 p. 356 (1959) also disclose phosphine addition to olefins in the liquid phase in the presence of non-oxidizing acids. Mono- and di-alkylated products were reported, however, the process required the use of 20-40 atm. pressures.
U.S. Pat. No. 4,922,025 discloses the production of organophosphines over a zeolitic catalyst in an autoclave having high pressures therein. See also W. Hoelderich, et al., Proc. Int. Congress on Catalysis, 9th, 1, 316-22 (1988).
U.S. Pat. No. 4,163,760 discloses a continuous, liquid phase, free radical, catalyzed process for the production of organic phosphines over an azobisisobutyronitrile and reactor pressures of 80-300 bar.
Stiles, A.R. (JACS 84, 3282 (1952)) also discloses the preparation of organophosphines by free radical catalyzed addition of olefins to PH.sub.3 through the use of radiation and sensitizers.
Free radical and acid catalyzed additions of olefins to phosphine give different products, which are the result of anti-Markonikov and Markonikov addition, respectively. Thus, free radical catalyzed addition of 2-methyl-1-propene to phosphine produces predominantly mono-iso-butylphosphine, whereas acid catalyzed addition of 2-methyl-1-propene to phosphine produces predominantly mono-tertiary-butylphosphine. Accordingly, the free-radical catalyzed processes are not useful to make mono-tertiary-butylphosphine or other mono-alkylphosphines comprising tertiary carbon-phosphorus linkages.
The methods used in the prior art to carry out acid catalyzed additions of olefins to phosphine, including those noted above, are typically low yield batch processes which require high reaction temperatures and/or high reaction pressures. Use of these processes further requires product purification and involves the generation of waste streams of significant quantities, the recycle or proper disposal of which pose significant problems in the current environment.
It is therefore an object of the present invention to provide a process for the production of alkylphosphines and especially mono-alkyl phosphines by acid catalyzed addition of olefins to phosphine, which may be run in a continuous fashion. It is a further object of the present invention to provide a process which does not involve high reaction pressures. It is still further an object of the present invention to provide a process which produces a high yield of product of relatively high quality, thereby obviating the necessity of costly purification procedures. It is still another object of the invention to provide a process which does not require disposal of significant quantities of reactants and/or byproducts.